1. Field of the Invention
The present invention relates to a method of, and an apparatus for, calculating the strength of an electromagnetic field radiated from an electric device according to a moment method, as well as a medium for storing a program to perform the method. In particular, the present invention relates a method of and an apparatus for precisely calculating, through user-friendly operations, the strength of an electromagnetic field radiated from two-wire cables laid in an electric device, as well as a medium for storing a program to perform the method.
Many countries have severe restrictions on electric devices to prohibit them from radiating radio waves and noise that exceed specific levels.
To meet the restrictions, many shielding and filtering techniques have been developed. These techniques need a technique for quantitatively evaluating the effect thereof.
The present inventors have disclosed several techniques for simulating the strength of an electromagnetic field radiated from an electric device with the use of the moment method. These techniques need a correct model of a target electric device.
2. Description of the Related Art
The strength of an electromagnetic field radiated from an object is simulated by finding electric and magnetic currents flowing through parts of the object and by substituting the currents in known electromagnetic formulae. The electric and magnetic currents flowing through parts of an object are calculable by solving Maxwell's electromagnetic equations under given boundary conditions.
The moment method is based on some integral equations derived from the Maxwell's electromagnetic equations. The moment method divides an object into small elements and calculates electric and magnetic currents flowing therethrough. The moment method is applicable to three-dimensional objects having optional shapes. The moment method is described in, for example, "Sinusoidal Reaction Formulation for Radiation and Scattering from Conducting Surface" by H. N. Wang, J. H. Richmond, and M. C. Gilreath in IEEE Transactions Antennas and Propagation, Vol. AP-23, 1975.
The moment method divides the structure of a target electric device into meshes and selects a frequency. Based on the frequency, the moment method calculates the mutual impedance, mutual admittance, and mutual reaction of the meshes. These data pieces and wave sources specified by structural data of the electric device are substituted for the simultaneous equations of the moment method, to provide electric and magnetic currents flowing through the meshes.
When handling a metal object, the moment method divides the metal object into meshes and finds mutual impedance Zij of the meshes. Linear equations of the moment method express the mutual impedance Zij, wave sources Vi, and currents Ii flowing through the meshes as follows: EQU [Zij][Ii]=[Vi]
where [ ] indicates a matrix. Solving this provides the currents Ii with which the moment method calculates the strength of an electromagnetic field radiated from the metal object.
If the meshes involve resistors, capacitors, and reactance elements, they are added to self-impedance components of the meshes.
Electric devices contain cables to connect two separate points to each other.
Conventional apparatuses and methods for calculating the strength of an electromagnetic field have no user interfaces for handling such cables laid in electric devices. The prior arts treat the cables as fixed parts and create models of the electric devices for the moment method.
These cables, however, have a large degree of freedom in their arrangements. They are bent and twisted between two points to connect, and they radiate strong electromagnetic fields.
The prior arts that treat cables as fixed parts are incapable of properly simulating electromagnetic fields radiated therefrom. The prior arts are also incapable of varying the arrangements of cables to determine the effect thereof.
There are many types of cables such as parallel cables and stranded cables, and there are different standards for these cables.
The prior arts, however, have no standardized theories to model cables, and therefore, must individually cope with a variety of cables whenever they are given. In particular, the prior arts provide no technique for modeling stranded cables. What is needed is a technique of precisely modeling various types of cables.